This invention relates generally to the field of optical communications and in particular to a method and apparatus for providing optical wavelength conversion employing cross phase modulation (XPM).
All optical wavelength converters which operate at speeds beyond the limits of electronic devices will be essential components in future Wavelength-Division-Multiplexed (WDM) networks. As was shown in a paper entitled xe2x80x9cWavelength Conversion at 10 GBit/s Using a Semiconductor Optical Amplifierxe2x80x9d which appeared in Photon Technol. Lett., 5, (11), pp. 1300-1303, (1993), J.M.Weisenfeld demonstrated all optical wavelength conversion using semiconductor optical amplifier (SOA) devices exploiting cross gain modulation (XGM) as well as cross phase modulation (XPM). As shown therein, in the XGM scheme a strong input signal and a cw signal are introduced into a nonlinear element. The input signal is used to saturate the gain of the nonlinear element and thereby modulates the cw signal carrying the new wavelength. In the XPM scheme, a strong input signal is used to modulate both the phase and intensity of a second signal. The modulation of this second signal is then exploited in an interferometric configuration for redirecting the signal from one output to an other.
Different interferometric configurations have been proposed. Some are based on Michaelson (MI), others are based on Mach-Zehnder interferometer (MZI) configurations with the nonlinear elements on one or both branches of the interferometer arms. (See, e.g., K. Tajima, xe2x80x9cAll Optical Switch with Switch Off Time Unrestricted by Carrier Lifetime; Jpn. J. Appl, Phys. Vol., 32, No. 12A, pp. L1746-1749; December 1993; K. E. Stubkjaer, T. Durhuus, B. Mikkelsen, C. Joergensen, R. J. Pedersen, C. Braagaard, M.Vaa, S. L. Danielsen, P.Doussiere, G. Garabedian, C. Graver, A. Jourdan, J. Jacquet, D. Leclerc, M. Erman, and M. Klenk, xe2x80x9cOptical Wavelength Convertersxe2x80x9dProc. European Conf. on Opt. Communication, Firence, Italy, Vol., 2, 635-642, September 1994; J.M.Weisenfeld, xe2x80x9cWavelength Conversion for Optical Networksxe2x80x9d, Second Optoelectronic and Communications Conference (OECC97), Technical Digest, pp. 426-427, July 1997. Recent developments include hybrid wavelength converters, using only a single SOA followed by a delay-interference section, formed by a calcite crystal. (See, Y. Ueno, S. Nakamura, K. Tajima, S. Kitamuraxe2x80x9d, xe2x80x9c3.8 THz Wavelength Conversion of Picosecond Pulses Using a Semiconductor Delayed-Interference Signal-Wavelength Converter (DISC)xe2x80x9d, Photon. Technol. Letters, Vol., 10, No. 3, March 1998; Y. Ueno, K. Tajima, xe2x80x9cWavelength Converterxe2x80x9d, EP 0 875 782 A2.
Despite these advances however, these delay interference wavelength converter schemes is hybrid in nature and their operation is fairly limited.
We have developed an integrated wavelength converter with a monolithically integrated delay loop in a delayed interference configuration that needs only one SOA, only one in and one output fiber. Unlike prior-art hybrid wavelength converters, our inventive device has a monolithically integrated delay loop utilizing an asymmetric splitting ratio.